The present invention relates to thermally responsive or thermostatically operated valves and particularly relates to thermostatically operated expansion valves of the type employed for controlling flow of refrigerant in an air conditioning or refrigeration system. In air conditioning systems employed for passenger compartment cooling of motor vehicles, it is known to employ an expansion valve for controlling refrigerant flow from the high pressure side of the compressor through the condenser to the evaporator by utilizing a valve which is moved by the force of expansion of fluid in a closed chamber which senses the temperature of the flow discharging from the evaporator. Such valves are referred to as thermostatic expansion valves and have found widespread use in automotive air conditioning systems.
Currently, it is becoming increasingly popular to provide dual evaporators in a single automotive air conditioning system such as one for front seat passengers and another for rear seat passengers; or, alternatively separate evaporators for cooling left and right seat row positions such as for the driver and front seat passenger. Where dual evaporators are employed, it has been desired to provide a way or means of shutting off one of the evaporators remotely with an electrically operated device without incurring the cost penalty of providing separate electrically controlled shut off valves in the refrigerant line to the evaporators.
The thermostatically controlled mechanical expansion valves presently employed in automotive air conditioning systems have experienced widespread usage because of their low cost and simplicity of construction. However, thermostatically controlled expansion valves are only able to react to temperature changes in the flow of refrigerant discharging from the evaporator; and, there is no way to provide external user control of the valve once it has been calibrated and installed in the system. It has been desired to provide remote electrical control of the vehicle air conditioning system to provide the user with a greater degree or level of control and to not rely only on the ability of the thermostatic expansion valve to provide proper control by reacting to evaporator discharge temperature.
Furthermore, it has been desired to provide for electrical control of refrigerant flow in a refrigeration or air conditioning system which enables the use of a microcomputer to employ selected algorithms to provide control of refrigerant flow in a manner providing improved cooling control.
Thus, it has been desired to provide a way or means of remotely electrically controlling the flow of refrigerant to plural evaporators in a vehicle air conditioning system. It has further been desired to provide for remotely shutting off the flow of refrigerant to one of a plurality of evaporators in a vehicle air conditioning system in a manner which is sufficiently low in cost to render the system cost effective in the high volume motor vehicle marketplace.